The fanatics are “radicalising” vulnerable inmates in what the Prison Officers’ Association calls a “real problem”.

Experts say they are turning jails into “state-funded breeding grounds for extremism”.

There are more than 11,000 Muslim prisoners.

Professor Anthony Glees, of the University of Buckingham, slammed the prison service’s “totally inadequate” screening of imams. He said: “It is completely unacceptable that imams with extreme views are allowed to preach in prisons.”

Ghaffar Hussain, of anti-extremism think tank Quilliam, added: “We are aware of several people employed by the prison service who have links to extremist groups.

“Young men are going in petty criminals and coming out extremists.”

Ghaffar Hussain

“Young men are going in petty criminals and coming out extremists.”

Among the groups is one which believes adulterers should be killed, while a preacher connected to prison chaplains condones beating women to “bring them to goodness”.

Steve Gillan, general secretary of the Prison Officers’ Association, said: “The prison service have had their fingers burnt on a few occasions when it was discovered some imams they employed had extreme views.”

A spokesman for the prison service said: “We are committed to tackling extremism in prison.”

Meanwhile, Islamic Isis militants are making a whopping £600,000 a day selling oil from captured Iraqi oil fields.